The present invention relates to a device and method for wireless energy transfer.
The search for wireless power transfer techniques is as old as the invention of electricity. From Tesla, and through the vast technological development during the 20th century, many suggestions have been proposed and implemented in this field of research. Established techniques of performing wireless energy transfer are known both in the near and far field coupling regimes. Near field examples can be found in optical waveguides, cavity couplers and in resonant inductive electric transformers. For the far field, one has power beaming mechanisms, where power is beamed at a receiver and is converted to usable electrical energy. These techniques, though they reach sufficiently high efficient energy transfer, suffer either from short range interaction (near field coupling), or from the requirement of line of sight in the far field approaches.
Recently, it has been shown that a weakly radiative wireless energy transfer scheme between two identical classical resonant objects is possible with sufficiently high efficiency. This possibility arises from employing coupled mode theory in the realm of power transfer. In this research Kurz et. al showed that wireless energy can be transferred efficiently over a 2 meter range, generally considered in this field as mid-range. This technique was adopted by others as well, where the transfer efficiency was increased tremendously from an efficiency of 40%, previously the best achieved for this range, to recently achieved values of around 75%, notably by Intel.
Currently, most efficient wireless energy transfer devices rely on a resonant constraint. Such a constraint typically means that when the frequency of the source is shifted from the frequency of the device, intentionally or due to random noise, a significant reduction of the efficiency of the wireless energy transfer would occur. Random noise may be the result of an external object being placed close to either of the coils When the resonance condition is violated, then one may need to provide a feedback circuit in order to avoid a possible reduction of the energy transfer.